Sodium vapor trap

ABSTRACT

A sodium vapor trap for sealing a rotary shaft to a housing, the trap having a stationary member carried by the housing and surrounding the shaft and a rotary member carried by the shaft for rotation within the stationary member, the rotary member and the stationary member having transverse baffles cooperating to provide a tortuous passageway communicating the interior of the housing with the exterior and forming a reflux condenser for condensing the sodium vapor to liquid sodium and returning it to the housing.

United States Patent 1 3,630,529

[72] Inventor Rowland E. Ball 2,981,490 4/1961 Conley 277/71 UXLongBeach,Calif. 2,600,991 6/1952 Hargrove 277/54X gp- 3 5 1 FOREIGNPATENTS [22 Pic ay Patented M18 1971 966,442 8/1957 Germany 277/53 [73]Assignee Borg-Warner Corporation Primary Examiner-Samuel B. Rothberg Chia 1]], AttorneysDonald W. Banner, William S. McCurry and John W. Butcher[54] SODIUM VAPOR TRAP 8 Claims, 3 Drawing Figs. ABSTRACT: A sodiumvapor trap for sealing a rotary shaft to a housing, the trap having astationary member carried by the [52] U.S.Cl 277/22, housing andSurrounding the Shaft and a rotary member can 277,56 165,73 ried by theshaft for rotation within the stationary member, the

[51] Int. Cl F02f ll/00, rotary member and the Stationary member havingtransverse F16] 15/00 baffles cooperating to provide a tortuouspassageway commu- [50] Field of Search 277/53-57,

137/254 mcating the interior of the housing with the exterior andforming a reflux condenser for condensing the sodium vapor to 56]References Cited liquid sodium and returning it to the housing.

UNITED STATES PATENTS 1,634,246 6/1927 Jones et a1. 277/133 X BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates to asodium vapor trap for sealing a rotary shaft to a housing having a shaftopening with a rotary shaft extending thcrethrough. More particularly,the invention relates or pertains to such a trap for mounting between avertical shaft and a housing surrounding it. The sodium vapor trap ofthe present invention is adapted to prevent the escape of sodium vaporalong the vertical shaft of a liquid sodium pump from the space withinthe pump to the space outside the pump.

2. Description of the Prior Art Certain liquid sodium pumps of the priorart have included a centrifugal impeller driven by a vertical shaftextending above the impeller through a pump barrel and passing through ashaft opening in the head of the barrel. The shaft is driven by anelectric motor mounted on the top of the barrel. A shaft seal, of themechanical seal type, and shaft bearings have been provided between thehead of the pump barrel and the electric motor thereabove. The shaftseal has prevented the escape of argon used as protective atmosphereover the liquid sodium in the pump. The impeller shaft rotates in a tubethat is spaced with a close clearance from the shaft and sealed bytransverse partitions at the top and bottom of the tube to the interiorof the pump barrel. The space enclosed by the upper and lowerpartitions, the shaft tube, and the pump barrel is filled withinsulation or shielding material to prevent or minimize the escape ofsodium vapor and to block radiation, if the sodium is radioactive.However, the space between the shaft and the shaft tube is open at thebottom to the sodium-vapor-containing atmosphere above the liquid sodiumin the pump, and is open at the top to allow escape of sodium vapor intothe mechanical seal compartment thereabove. Such sodium vapor asmigrates into the mechanical seal compartment condenses therein to solidsodium and interferes with the proper functioning of the seals.

SUMMARY OF THE INVENTION An object of the invention is to provide asodium vapor trap for substantially eliminating the escape of sodiumvapor from a housing along a shaft, such as a pump impeller shaft, thatextends into the housing through a shaft opening.

A further object is to provide such a trap that will act as a refluxcondenser to condense the sodium vapor to liquid and return it as aliquid to the housing.

The foregoing and other objects of the invention are attained in asodium vapor trap for sealing a rotary shaft to a housing having a shaftopening with a rotary shaft to a housing having a shaft opening with arotary shaft extending therethrough, the trap substantially preventingthe escape of sodium vapor along the shaft from the space within thehousing to the space outside the housing, the trap comprising: a rotarymember carried by and sealed to the shaft; a stationary membersurrounding the rotary member and carried by and sealed to the housing;the rotary member having axially spaced, transverse baffles projectingaway from its axis; and the stationary member having axially spaced,transverse baf fles projecting toward its axis and cooperating with thefirstmentioned baffles to provide a tortuous passageway communicatingthe space within the housing with the space outside the housing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an axial, sectional view ofportion of a sodium pump with a sodium vapor trap in accordance with theinvention installed therein;

FIG. 2 is an enlarged axial sectional view of a portion of the structureof FIG. 1 that shows in section the sodium vapor trap shown in elevationin FIG. 1; and

FIG. 3 is a sectional view on a reduced scale taken along the line 3-3of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the several figures of thedrawings and in the following description, the same part is alwaysdesignated by the same reference numeral.

Referring to the drawings, particularly to FIG. 1, there is shown aportion of a liquid sodium pump having a pump barrel 10 with a flange llwelded to its top. A head 12 is sealed to the flange 11 by an O-ring 13.An annular, ring-shaped member 14 is supported upon the head 12 and issealed to the latter by another O-ring 15. The member 14 supports aconcentric ring 16, the two members being sealed to each other by yetanother O-ring 17. A cylindrical housing member 18 is welded to the topof the ring 16, the housing member 18 supporting an electric motor (notshown) which drives the pump impeller (not shown) through a shaft 19, asis conventional. Bolts 21,21 having nuts 22,22 are employed to securetogether the concentric annular ports 1 1, 12, 14 and 16.

A dome 23 is welded to the annular, ring-shaped member 16 and has asleeve 24 welded to it and surrounding the shaft 19, as more clearlyseen in FIG. 2.

As shown in FIG. 1, a transverse plate 25 is welded to the housingmember 18 and is positioned above the dome 23. This plate 25 carries acollar 26 providing a seat for a mechanical seal assembly designated bythe general reference numeral 27 and having a stationary subassembly 28and a rotary subassembly 29 carried by the shaft 19. The stationarysubassembly has a nonrotating mechanical seal ring 30. In rotatingsealing relationship to this seal ring is a rotary mechanical seal ring31. Referring to FIG. 2, there is a chamber 32 in the stationarysubassembly 28 that is filled with oil under a static pressure somewhatabove the static pressure of the gas in the space 33 below themechanical seal assembly and above the dome 23. This mechanical sealassembly prevents the escape of gas along the shaft from below themechanical seal assembly to the atmosphere. As a mechanical sealassembly of this type is known in the prior art, a further detaileddescription thereof is not deemed necessary herein.

The rotating subassembly 29 of the mechanical seal has a depending skirt61 carrying a flange or flinger 62 that rotates with the shaft. Any oilthat seeps past the seal rings 30,31 is caught by the flinger 62 andspun outwardly into the chamber 63. As seen in FIG. 1, a conduit 64drains the oil from the chamber 63 into a sump 65 from which it may bewithdrawn upon removal of the plug 66. Thus, oil is prevented fromflowing downwardly along the shaft into the sodium pump.

Turning to FIG. 2, it is seen that the shaft 19 has a lower section 19asecured to an upper section 1% by screw 34, the two shaft sections beingprevented from relative rotation by a key 35.

A sodium vapor trap designated by the general reference numeral 36 isinterposed between the shaft 19 and the head 12 for the purpose ofsubstantially preventing the escape of sodium vapor along the shaft andacross the head. The sodium vapor trap has a stationary member 37carried by the head 12 and a rotary member 38 carried by the shaft 19;these members preferably are fabricated from austenitic stainless steel.

The rotary member 38 has a cylindrical portion 39 fitted to the shaftsection 19b. A reduced-diameter portion 41 of the rotary member isreceived in a corresponding rabbet 42 in the shaft section 19a. Therotary member is locked to the shaft section by a set screw 43. Thecylindrical section 39 carries axially spaced, outwardly projecting,downwardly sloping baffles in the form of fins 44. These fins are bodiesof revolution and have the same outer diameters; they are evenly spacedin the axial direction and sloped downwardly at an angle ofapproximately 30 from the horizontal. The rotary member 38 has a capportion 45 with a horizontal top 46 and depending skirt 47. The capoverlies the stationary member 37 and is spaced slightly therefrom sothat it may rotate freely and without interference and yet provide forthe outward flow of gas between the stationary and rotary members of thetrap. An O-ring 48 seals the rotary member to the lower shaft section19a. It will be seen that the fins 44 have a uniform thickness.

The stationary member 37 of the trap is welded to the barrel head 12.The stationary member is generally cylindrical. it has a bottom portion49 that closely encircles the shaft section 190 and underlies the bottomportion of the rotary member 38. The portion 49 receives the upper endof a tube 51 that encompasses the lower section 19a of the shaft and isspaced therefrom to provide a clearance 52. The upper end of the tube 51is received in a recess 53 in the bottom portion of the stationarymember and is welded therein. The stationary member 37 has a pluralityof inwardly projecting baffle members 54 positioned opposite to thespaces between the fins 44 on the rotary member. These baffle membershave generally horizontal bottom surfaces 55, cylindrical inner surfaces56, and downwardly sloping upper surfaces 57. The inner diameters of thebaffle members are equal and slightly greater than the outer diametersof the fins 44 of the rotary member; this enables the rotary member tobe inserted into and removed from the stationary member.

In operation, the sodium vapor trap 36 acts as a reflux condenser forthe sodium vapor that rises through the clearance space 52 between theshaft section 190 and the tube 51. This sodium vapor is carried in aninert atmosphere such as an atmospheie of argon, the argon beingemployed to prevent oxidation of the sodium and sodium vapor in thepump. The sodium vapor passing between the rotary and stationary membersof the trap is deflected by the fins and baffle members against theinternal surfaces of the trap upon which the sodium vapor is condensedto the liquid state,, the liquid flowing downwardly along the internalsurfaces of the trap and returning towards the pump through theclearance space 52.

Although the specific configuration of the fins 44 and baffle members 54may be varied somewhat, the interior surfaces of the trap componentsshould be so sloped that all of the condensed metal will flow back tothe pump; preferably there should be no recesses in the trap to retaincondensed metal. The shape and disposition of the fins 44 tends todirect the flow of argon and sodium vapor substantially normally uponthe upper faces 57 of the baffle members 54. These surfaces 57 are theprincipal condensing surfaces of the trap; they are cooled more rapidlythan the fins 44, as the heat radiates outwardly from the radial outersurfaces of the stationary member 37. Condensation of sodium vapor andradiation from the trap maintain the condensing surfaces of the trapslightly to somewhat above the melting point ofsodium, namely, 995 C.The trap of the present invention is extremely efficient, andsubstantially no sodium vapor exits from the trap into the space beyondthe trap. Moreover, because the sodium vapor condenses to a liquid, andnot to solid metal, the interior of the trap does not become cloggedwith condensed solid metal. Rotation of the shaft, and with it therotary member 38 of the trap, promotes high condensation efficiency. Therotary motion causes the gasses to impinge on the stationary member withhigher velocity than would be the case without such rotation. Thishigher velocity improves condensation. Although the trap is moreefficient when the member 38 rotates, it nevertheless is an effectivereflux condenser when the member 38 is stationary.

With the present invention, sodium vapor from the pump cannot escape toany appreciable extent and condense as liquid or solid metal in andaround the shaft and mechanical seal assembly.

Although the specific embodiment of the invention herein shown anddescribed has been described with reference to the condensation ofsodium vapor, it will be understood that the trap can also be employedto condense other metal vapors, more particularly alkali metal vapors,and specifically vapors of potassium or sodium-potassium alloys known asNAK. Therefore, the term sodium is used herein in a generic sense, andis not intended to limit the invention to the condensation of sodiumvapor, but is intended to be broadly construed to include other alkalimetals and alloys thereof.

The number of alternate fins and baffle members may be more or less thanthe four shown in the drawings.

lclaim: l. A sodium vapor trap for sealing a rotary shaft to a housinghaving a shaft opening with a rotary shaft extending therethrough, saidtrap substantially preventing the escape of sodium vapor along the shaftfrom the space within the housing to the space outside the housing, saidtrap comprising:

a. a rotary member carried by and sealed to the shaft;

b. a stationary member surrounding said rotary member and carried by andsealed to the housing;

c. said rotary member having axially spaced, transverse bafflesprojecting away from its axis;

d. said stationary member having axially spaced, transverse bafflesprojecting toward its axis and cooperating with said first-mentionedbaffles to provide a tortuous passageway communicating the space withinthe housing with the space outside the housing; said membersconstituting means for maintaining said trap at a temperature above themelting point of said sodium such that vapor thereof between saidmembers is condensed to the liquid state,

f. said baffles sloping downwardly toward the interior of the housingsuch that the condensed liquid sodium flows freely into the space withinthe housing.

2. A sodium vapor trap as defined in claim 1, wherein said bafiles arebodies of revolution.

3. A sodium vapor trap as defined in claim 1, wherein saidfirst-mentioned baffles alternate with said second-mentioned baffles.

4. A sodium vapor trap as defined in claim 1, wherein said rotary memberhas a cap portion surrounding and spaced from the axially outer end ofsaid stationary member.

5. A sodium vapor trap as defined in claim 1, wherein said stationarymember has an axially inner end portion underlying the axially inner endofsaid rotary member.

6. A sodium vapor trap as defined in claim 1, wherein saidfirst-mentioned bafi'les are slightly smaller in diameter than saidsecond-mentioned baffles.

7. A sodium vapor trap as defined in claim 1, wherein said memberscomprise austenitic stainless steel.

8. A sodium vapor trap as defined in claim 1, wherein said members aredisposed vertically about a vertical shaft.

1. A sodium vapor trap for sealing a rotary shaft to a housing having ashaft opening with a rotary shaft extending therethrough, said trapsubstantially preventing the escape of sodium vapor along the shaft fromthe space within the housing to the space outside the housing, said trapcomprising: a. a rotary member carried by and sealed to the shaft; b. astationary member surrounding said rotary member and carried by andsealed to the housing; c. said rotary member having axially spaced,transverse baffles projecting away from its axis; d. said stationarymember having axially spaced, transverse baffles projecting toward itsaxis and cooperating with said first-mentioned baffles to provide atortuous passageway communicating the space within the housing with thespace outside the housing; said members constituting e. means formaintaining said trap at a temperature above the melting point of saidsodium such that vapor thereof between said members is condensed to theliquid state, f. said baffles sloping downwardly toward the interior ofthe housing such that the condensed liquid sodium flows freely into thespace within the housing.
 2. A sodium vapor trap as defined in claim 1,wherein said baffles are bodies of revolution.
 3. A sodium vapor trap asdefined in claim 1, wherein said first-mentioned baffles alternate withsaid second-mentioned baffles.
 4. A sodium vapor trap as defined inclaim 1, wherein said rotary member has a cap portion surrounding andspaced from the axially outer end of said stationary member.
 5. A sodiumvapor trap as defined in claim 1, wherein said stationary member has anaxially inner end portion underlying the axially inner end of saidrotary member.
 6. A sodium vapor trap as defined in claim 1, whereinsaid first-mentioned baffles are slightly smaller in diameter than saidsecond-mentioned baffles.
 7. A sodium vapor trap as defined in claim 1,wherein said members comprise austenitic stainless steel.
 8. A sodiumvapor trap as defined in claim 1, wherein said members are disposedvertically about a vertical shaft.